2,3,7,8-tetrachlorodibenzo-p-dioxin and diindolylmethanes differentially induce cytochrome P450 1A1, 1B1, and 19 in H295R human adrenocortical carcinoma cells

Diindolylmethane (DIM) is an acid-catalyzed condensation product of indole- 3-carbinol, a constituent of cruciferous vegetables, and is formed in the s tomach. DIM alters estrogen metabolism and inhibits carcinogen-induced mamm ary tumor growth in rodents. DIM is a weak agonist for the aryl hydrocarbon (Ah) receptor acid blacks the effects of estrogens via inhibitory Ah recep tor-estrogen receptor cross-talk. DIM and various structural analogs were e xamined in H295R cells for effects on 3 cytochrome P450 (CYP) enzymes invol ved in estrogen synthesis and/or metabolism: CYP1A1, CYP1B1, and CYP19 (aro matase). Aromatase activity was measured by conversion of 1 beta-H-3-andros tenedione to estrone and (H2O)-H-3. H295R cells were exposed to the test ch emicals dissolved in dimethyl sulfoxide for 24 h prior to analyses. 2,3,7,8 -Tetrachlorodibenzo-p-dioxin (TCDD) (0-30 nM) and DIM (0-10 muM) induced et hoxyresorufin-O-deethylase (EROD) activity, as a measure of CYP1A1 and poss ibly 1B1 activity, with EC50 values of about 0.3 nM and 3 muM, respectively , DIM, but not TCDD, induced aromatase activity with an apparently maximal 2-fold increase at 10 muM; higher concentrations of DIM and many of its ana logs were cytotoxic. TCDD (30 nM) significantly increased CYP1A1 and 1B1 mR NA levels, but had no effect on mRNA for CYP19. DIM (3 muM) significantly i ncreased mRNA levels for all three CYPs. DIM analogs with substitutions on the 5 and 5' position (3 muM) induced aromatase and EROD activity, together with mRNA levels of CYP1A1, 1B1, and 19; analogs that were substituted on the central carbon of the methane group showed little or no inductive activ ity toward the CYPs. In conclusion, DIM and several of its analogs appear t o induce CYPs via multiple yet distinct pathways in H295R human adrenocorti cal carcinoma cells.